It has been known for some time that drugs and medical instruments and implements have to be irradiated so that they will not cause patients to become ill from harmful bacteria when they are applied to the patients. Systems have accordingly been provided for irradiating drugs and medical instruments and implements. The drugs and the medical instruments and implements have then been stored in sterilized packages until they have been ready to be used.
In recent years, it has been discovered that foods can carry harmful bacteria if they are not processed properly or, even if they are processed properly, that the foods can harbor and foster the proliferation of such harmful bacteria if they are not stored properly or retained under proper environmental conditions such as temperature. Some of the harmful bacteria can even be deadly.
For example, harmful bacteria have been discovered in recent years in hamburgers prepared by one of the large hamburger chains. Such harmful bacteria have caused a number of purchasers of hamburgers at stores in the chain to become sick. As a result of this incident and several other similar incidents, it is now recommended that hamburgers should be cooked to a well done state rather than a medium rare or rare state. Similarly, harmful bacteria have been found to exist in many chickens that are sold to the public. As a result of a number of incidents which have recently occurred, it is now recommended that all chickens should be cooked until no blood is visible in the cooked chickens.
To prevent incidents such as discussed in the previous paragraphs from occurring, various industries have now started to irradiate foods before the goods are sold to the public. This is true, for example, of hamburgers and chickens. It is also true of fruits, particularly fruits which are imported into the United States from foreign countries.
In previous years, gamma rays have generally been the preferred medium for irradiating various articles. The gamma rays have been obtained from a suitable material such as cobalt and have been directed to the articles to be irradiated. The use of gamma rays has had certain disadvantages. One disadvantage is that irradiation by gamma rays is slow. Another disadvantage is that irradiation by gamma rays is not precise. This results in part from the fact that the strength of the source (e.g. cobalt) of the gamma rays decreases over a period of time and that the gamma rays cannot be directed in a sharp beam to the article to be irradiated. This prevents all of the gamma rays from being useful in irradiating the articles.
In recent years, electron beams have been directed to articles to irradiate the articles. Electron beams have certain advantages over the use of gamma rays to irradiate articles. One advantage is that irradiation by electron beams is fast. For example, a chub having a square cross section can be instantaneously irradiated by a passage of an electron beam of a particular intensity through the chub. Another advantage is that irradiation by an electron beam is relatively precise because the strength of the electron beam remains substantially constant even when the electron beam continues to be generated over a long period of time.
X-rays have also been used to irradiate articles. The x-rays may be formed from electron beams. An advantage in irradiating articles with x-rays is that the articles can be relatively thick. For example, x-rays can irradiate articles which are thicker than the articles which are irradiated by electrons.
A problem has occurred in the past whether the irradiation has been provided by gamma rays, electrons or x-rays. This has occurred when the articles have had irregular characteristics such as irregular geometrical configurations. For example, a chub is generally circular in vertical section. This has caused the thickness of the chub to be different at every position in a radial direction in the cylindrical shape of the chub. These differences in thickness have affected the radiation which the chubs have received at the different positions.
The radiation received at every position in an article should be within particular minimum and maximum limits. If the radiation received at any position within the article is below the particular minimum limit, the harmful bacteria in the article are not destroyed. If the radiation received at any position in the article is above the particular maximum limit, quality or organoleptic characteristics of the article may be adversely affected. It is difficult to maintain the radiation dose in the article within the particular minimum and maximum limits when the article has irregularities in the characteristics at the different positions such as irregularities in the geometric configuration of the article. For example, a chub having a cylindrical configuration may be considered to have irregularities in characteristics because the vertical dimensions of the chub at the progressive positions of the chub in the horizontal direction are different.